[PATCH] libstdc++: Ignore filesystem::canonical errors for /etc/localtime [PR125467]

While the errors from realpath (and readlink before r17-2048-gcc195f7b11a406)
are ignored (str is left empty), the filesystem::canonical path thrown
exception in such situation. This patch ignores the error consistently,
by using error_code overload of filesystem::canonical.

The !ec check before str assignment is not necessary, as standard requires
that filesystem::canonical returns empty path, but I think it helps
readability.

libstdc++-v3/ChangeLog:

	PR libstdc++/125467
	* src/c++20/tzdb.cc (tzdb::current_zone): Use error_code overload
	of filesystem::canonical to ignore errors.
---
I agree there is inconsistency in treatment of filesystem errors, and
they seem to be consistently ignored on other paths. Torbjorn could you
confirm that this addresses the issue.
We will still need to wait for Jonathan to OK this.

Not sure how to test this branch. But tested this change locally.
OK for trunk?

 libstdc++-v3/src/c++20/tzdb.cc | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/src/c++20/tzdb.cc b/libstdc++-v3/src/c++20/tzdb.cc
index e358b778e2d..0d004a8a6fe 100644
--- a/libstdc++-v3/src/c++20/tzdb.cc
+++ b/libstdc++-v3/src/c++20/tzdb.cc
@@ -2335,8 +2335,10 @@ constinit tzdb_list::_Node::NumLeapSeconds tzdb_list::_Node::num_leap_seconds;
 	str = p;
       }
 #else
-    string sbuf = std::filesystem::canonical("/etc/localtime").string();
-    str = sbuf;
+    error_code ec;
+    string sbuf = std::filesystem::canonical("/etc/localtime", ec).string();
+    if (!ec)
+      str = sbuf;
 #endif
 
     if (!str.empty() && str != "/etc/localtime")
-- 
2.55.0